1. Field of the Invention
The invention relates to a speed changer.
2. Description of the Related Art
For example, for personal mobility and electric vehicles, a speed changer (gear unit) with a relatively high speed reducing ratio is used to output a high rotation torque using a small motor. As a speed changer that enables a high speed reducing ratio to be set, for example, a small-tooth-number-difference reduction gear and a strain wave gearing disclosed in Japanese Patent Application Publication No. S60-143244 (JP S60-143244 A) are known.
Conventional speed changers enable a speed change ratio (a speed reducing ratio and a speed increasing ratio) to be set to a desired value, but disadvantageously, the range of values that can be set (the range of selections) is narrow. Further disadvantageously, a significant change in speed change ratio needs a substantial change in design.